1. Field of Invention
This invention generally relates to voltage multipliers and more particularly to circuitry for providing a high level supply voltage from a relatively low voltage source used for supplying power to small electronic devices, such as time display circuitry suitable for use in electronic watches.
2. Description of Prior Art
Voltage multipliers in general are well known. A typical well known voltage multiplier employs capacitors and diodes to provide a voltage output which is twice the value of the peak A.C. input voltage. Such prior art devices, as will be described in greater detail hereinbelow, are unsatisfactory for use in low voltage applications because of the loss in voltage dropped across the diode or diodes. A more recent prior art voltage multiplier is described in U.S. Pat. No. 3,815,354 entitled "Electronic Watch," which issued June 11, 1974 to Richard L. Sirocka and David F. Broxterman. Such a prior art voltage multiplier employs transistor switching means, an inductive element, a capacitive element, and a diode; and, operates on the principle of inducing a relatively high voltage across an inductor by rapidly changing the current through the inductor. The output voltage is rectified and "smoothed" by the diode and capacitor. This prior art voltage multiplier is difficult to minitaurize and especially creates a space packaging problem when used in small devices, such as electronic watches, where it is always desirable to eliminate componants external to the integrated circuit.
Another prior art device for voltage multipliers is set forth in an article entitled "CMOS-Circuits for Digital Watches" by James Kerine, which was published in a seminar entitled "Electronic Watches," parts I and II of the 1975 Wescon Professional Program of San Francisco, Sept. 16, 1975.
In FIG. 5 of this article at page 4 thereof, a "Voltage Tripler" circuit is illustrated, which employs CMOS devices to multiply a small input voltage to a relatively high output voltage.